NAME

isalpha, isupper, islower, isdigit, isxdigit, isalnum, isspace, ispunct, isprint, isgraph, iscntrl, isascii − Classify characters

LIBRARY

Standard C Library (libc.a)

SYNOPSIS

#include <ctype.h>

int isalnum(
int c);

int isalpha(
        int c);

int isascii(
        int c);

int iscntrl(
        int c);

int isdigit(
        int c);

int isgraph(
        int c);

int islower(
        int c);

int isprint(
        int c);

int ispunct(
        int c);

int isspace(
        int c);

int isupper(
        int c);

int isxdigit(
        int c);

PARAMETERS

cSpecifies the character to be tested. In all cases, this parameter is an  int data type, whose value must be representable as an unsigned char or must equal the value of the macro EOF (defined in the stdio.h include file). When this parameter has a value that cannot be represented as an unsigned char or EOF, the result is undefined. 

DESCRIPTION

The ctype functions tests for membership in a character class in the current locale.  Each function tests to see if a character is part of a different character class. 

If the character is part of the character class, the function returns a nonzero value for true; otherwise, the function returns a value of 0 (zero) for false. 

Each function is named by adding the prefix is to the name of the character class for which the function tests. For example, the isalpha() function tests whether the character specified by the c parameter belongs to the alpha class. 

The following lists the function names and describes the conditions under which the functions return a true value. 

isalnum()When c is a character of class alpha or class digit in the program’s current locale. 

isalpha()When c is a character of class alpha in the program’s current locale. Characters in classes lower and upper automatically belong to class alpha. 

isascii()When c is a 7-bit US-ASCII character whose value is in the range 0 to 0177 (0 to 0x7F), inclusive. 

iscntrl()When c is a character of class cntrl in the program’s current locale. 

isdigit()When c is a character of class digit in the program’s current locale. The following characters are included in this class:

0 1 2 3 4 5 6 7 8 9

isgraph()When c is a character of class print in the program’s current locale. Characters in classes alpha, digit, and punct are automatically in class graph.  Unlike isprint(), isgraph() returns FALSE for the space character. 

islower()When c is a character of class lower in the program’s current locale. At a minimum, the 26 lowercase US-ASCII characters are included in this class. These are:

a b c d e f g h i j k l m n o p q r s t u v w x y z

isprint()When c is a character of class print in the program’s current locale. All characters in the class graph and the space character are automatically included in the class print. 

ispunct()When c is a character of class punct in the program’s current locale. 

isspace()When c is a character of class space in the program’s current locale. At a minimum, the space, form-feed, newline, carriage-return, tab, and vertical-tab characters are included in this class. 

isupper()When c is a character of class upper in the program’s current locale. At a minimum, the 26 uppercase US-ASCII characters are included in this class. These are:

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

isxdigit()When c is a character of class xdigit in the program’s current locale. The following characters are included in this class:

0 1 2 3 4 5 6 7 8 9 A B C D E F a b c d e f

NOTES

The LC_CTYPE category of the setlocale() function affects all conversions. 

In the C locale, or in a locale where character-type information is not defined, characters are classified according to the rules of the US-ASCII 7-bit coded character set. For any character value greater than octal 177 (0177 in C-language context) the value 0 (zero) is returned. 

AES Support Level:
Full use.

RETURN VALUES

Upon successful completion of any function, a nonzero (TRUE) value is returned.  Otherwise, the value 0 (FALSE) is returned. 

RELATED INFORMATION

Files: locale(4). 

Functions: ctype(3), setlocale(3), wctype(3).